Expression of Ki-67, Oct-4, γ-tubulin and α-tubulin in human tooth development

To analyze factors controlling cell proliferation and differentiation, and appearance of primary cilia during the cap and bell stages of incisor or/and canine human enamel organs.

Qualitative and quantitative analysis of proliferating Ki-67 positive cells and expression of γ-tubulin, α-tubulin and Oct-4 was immunohistochemically analyzed in the cap an bell stages of 10 developing human incisor and canine germs, 8-21 weeks old.

During the analyzed period, ratio of Ki-67 positive cells changed in outer enamel epithelium from 48.86% to 24.52%, in inner enamel epithelium increased from 56.11% to 60.06% and then dropped to 44.24%. While in dental papilla proliferation first increased from 46.26% to 55.45%, and then dropped to 22.08%, a constant decrease of proliferation characterized enamel reticulum (from 46.26% to 15.49%). Strong cytoplasmic Oct-4 expression characterized epithelial parts of enamel organ, particularly the differentiating ameloblasts. During further development, Oct-4 expression shifted to both nuclear and cytoplasmic expression in mesenchymal tooth components. Primary cilia characterized most of the cells in developing enamel organ. While non-ciliated (proliferating) cells mainly contained two centrioles (γ-tubulin), the primary cilia (α-tubulin) were arising from basal bodies (γ-tubulin) of non-proliferating cells.

We suggest that increase in cell proliferation enables growth of enamel organ, while its selective decrease leads to disintegration of some tooth parts. Drop of proliferation coincided with initiation of ameloblast and odontoblast differentiation. Additionally, cell differentiation was accompanied by increased expression of Oct-4 and probably by signalling via primary cilia, both regulating processes of cell proliferation and differentiation.